This invention relates to controllable pitch propeller assemblies and, more particularly, to bearings for journaling the propeller blades within the propeller hub.
The blades and their bearing support in the propeller hub of controllable pitch propeller assemblies are subjected to extremely high loading. This loading is the result of centrifugal forces which tend to move the blades outwardly during rotation, and of the axial forces caused by the thrust on the blades. The loading on the blades is transferred to the blade roots in the propeller hub where bearings are provided to permit turning motion of the blades. In order to support the loading on the blades with a minimum of deflection of the bearing support members, the bearing must be rigidly fixed to the propeller hub, yet have sufficient clearance to allow the necessary turning motion of the blades.
It is known to provide a controllable pitch propeller with a bearing support for the blades that includes a liner or sleeve positioned within bored radial holes in the propeller hub that journals the blades to support the rotating motion of the blades and bearing rings on the outer and inner ends of the bore to support the bending and radial loads on the blade. This type of bearing support requires many parts with closely machined tolerances in order to achieve the necessary support and to eliminate the slack caused by the cumulative tolerances of the parts. Moreover, such a bearing support requires that the propeller hub be machined on its inner surface where the inboard bearing ring is placed, and further that all the bearing parts be fixed to the hub by keys or other means.
Another known bearing arrangement includes a bearing ring, having threads on its outer circumferential surface that engage corresponding internal threads in a bore in the hub. In this arrangement, the threaded ring is secured or seated against a shoulder in the bore. Since the threads in this type of bearing are preloaded in one direction only when the ring is tightened against the shoulder, the ring has a tendency to work itself loose even when keyed or pinned.
The principal object of this invention is to provide a simplified bearing support for the blades of a controllable pitch propeller assembly that includes a threaded connection to the propeller hub and that is solidly locked to the hub.
Another object is to provide a bearing whose radial position in the propeller hub is easily adjusted to compensate for inaccuracies in machining or cumulative buildup of tolerances of the various parts.
Another object is to provide a bearing for the blades that is easily installed or removed, that permits easy assembly of the parts, and that does not require any machining work to be performed on the inside surface of the propeller hub.
A further object is to provide a bearing for the blades in a controllable pitch propeller assembly that has fewer parts than prior art bearings, that is of practical, durable and compact construction, and that is simple and inexpensive to manufacture.